Embryonic stem cells (ESCs) are derived from very early stage embryos. ESCs can be maintained in culture indefinitely while retain the ability to make any type of cell in the body. These properties make ESCs a very powerful tool to address basic biology questions. ESCs also offer an important renewable resource for future cell replacement therapies for many diseases such as Parkinson’s disease, spinal cord injury, etc. However, before the full potential of ESCs can be exploited in the clinic, we need to understand more about their biological properties so that we can control their fate towards either self-renewal or differentiation into a specific cell type required for cell replacement therapy. STAT3 is a major player in controlling the fates of a variety of cell types including ESCs. Recently we demonstrated that STAT3 has diverse and distinct roles in regulating cell fate in both mouse and human ESCs. In mouse ESCs, STAT3 is involved in cell adhesion, cell growth/survival and maintenance of self-renewal. Interestingly, STAT3 seems to have opposite roles in human ESCs. It induces growth arrest and differentiation of human ESCs. Why does the same factor play such diverse and contradictory roles between these very similar cells? The answer may lie on how STAT3 is in action. STAT3 is present in every type of cell. It contains six distinct functional regions. STAT3 can directly induce the expression of many genes. STAT3 can also cooperate with other proteins to regulate gene expression. We recently derived STAT3-/- ES cells in which the STAT3 gene was removed. These cells will provide us a powerful tool to dissect STAT3 function. We will first determine the role of each of its six functional regions. Then we will try to understand why they function differently. Is it because they induce different sets of genes, or because they cooperate with different partners? Understanding how STAT3 works is important for us to control the fate of ESCs, and for their eventual clinical application.

Statement of Benefit to California:

Human embryonic stem cells (hESCs) can reproduce themselves in a culture dish. They can also give rise to every cell type in the body. In the future, hESCs may hold the key to replacing cells lost in many devastating diseases such as Parkinson’s disease, spinal cord injury, etc. Before hESCs can be used clinically, however, we must learn more about how to control their fate. STAT3 is a key player in regulating ES cell fate. STAT3 is also involved in the pathogenesis of diverse human cancers. In this proposed research, we will use a unique tool developed by us to understand STAT3's function. Our work will lead to a better understanding how hESC fate is regulated, which will be an important step towards achieving the therapeutic potential of hESCs. We also expect that our research will have a great implication in developing effective cancer therapies against novel STAT3 targets identified in this study.

Review Summary:

This proposal is focused on dissecting the distinct roles of an intracellular mediator of cytokine signaling, STAT3, in embryonic stem cells (ESC). The proposal takes advantage of evidence that different domains of the molecule are responsible for different functions in stem cell self-renewal and differentiation. The principal investigator (PI) proposes to elucidate these different roles in order to utilize this knowledge to improve differentiation protocols for human and mouse ESCs. The research proposal is divided into three parts. First, the PI will dissect the molecular function of key domains of STAT3, taking advantage of Stat3 knockout ESCs. In the second aim, the PI will perform a yeast-two-hybrid screen with each of the key domains in order to identify STAT3 binding partners, to gain insight into how these domains function. In the last aim, the applicant will apply some of the observations made in the mouse studies to human ESCs. Overall, the proposal is focused on basic aspects of self-renewal and differentiation in ES cells, largely based on previous published work.
This is a well-written, highly focused proposal to dissect various pathways influenced by a pleiotropic transcription factor important in ESC biology. Thus, this proposal addresses a research subject of great significance. The work is appropriate for the time frame and will undoubtedly generate a lot of technical information about STAT3 in human and mouse ESCs that may be of fundamental importance to stem cell therapies. Some aspects of the proposal constitute a rather conventional follow up from what is already known, and it is unclear how much more novel information this project will provide. The tools used are solid but not very innovative, except for the availability of mouse ESCs that can be maintained in the absence of Stat3 function. This a unique tool, developed by the applicant, that is critical to the feasibility of this proposal. Reviewers raised questions about the significance of aim 3, since STAT3-mediated signaling is dispensable for human ESC self-renewal.
The PI trained as a post-doc with a pre-eminent stem cell researcher, a highly productive experience that led to the publication of several seminal papers that have relevance to this application. Furthermore, the PI is a recognized leader in the analysis of Stat3 function in ESC. The PI was recruited to the home institution as an Assistant Professor in 2006, and a short time later received a CIRM Grant in 2007. The PI is uniquely well suited to carry out the proposed studies. A comprehensive, well thought-out mentoring plan is presented, including a very strong letter of support from one of the mentors, a leading stem cell scientist. The career development plan lays out a framework for future studies relevant to ESC biology, but lacks a timeline or milestones. The institutional commitment to the PI is excellent, as the PI was provided with ample laboratory space and start-up funds. The institution has made a significant commitment to the stem cell field, as exemplified by the recent recruitment of a number of new investigators in the field of stem cell biology.
In conclusion, the applicant presented a solid proposal that aims to elucidate the molecular function of an important factor operating in ESC cells. The applicant was judged to be an accomplished young investigator, uniquely prepared to carry out the proposed studies.